Images show axial spin-echo proton density (on the right) and GRE (on the left) of the SN at level I of an ex vivo brain
sample in a 67-year-old woman. There is a triple-layered organization of the SN comparable to that showed in the in vivo images.
Ventrally a low-signal-intensity layer (b) is attributable to the pars reticulata of the SN. In the middle part of the SN, a hyperintense
band (c) corresponds to the ventral component of the pars compacta of the SN. The lateral part of this layer shows a high-signalintensity
spot (c1) corresponding to the oval shape hyperintensity of the in vivo three-dimensional multiecho susceptibility-weighted
images that resemble the nigrosome formation. The dorsal hypointense layer visible on both spin-echo and GRE images (d) is referred
to the dorsal component of the pars compacta of the SN. a = crus cerebri, e = brachjum conjunctivum, f = medial lemniscus,
g = lateral lemniscus, h = central tegmental tract.